the following info from an RPGamer.net Discussion Board:

Grelox writes:

I've done some research, and the Port 530 error (which I also get) seems to be caused by:
1) the user is behind a NAT (Network address translator) which happens if your using a router,
AND the FTP server is hosting on a non standard port (Not port 21).
Apparently there are fixes possible (the most easiest is probably asking the FTP server to serve on port 21) for people with NAT/Routers. Here are some links/explanations that do a good job of explaining it:

http://www.linksysftp.org/troubleshooting.php

http://www.dslreports.com/forum/remark,1381832
(This link says that the clients FlashFXP and BPFTP can do PORT Clients that can do PORT mode behind an NAT Firewall, anyone have these programs, get them working?)

http://linux.umbc.edu/lug-mailing-list/2003-06/msg00017.html
- Letter (http://linux.umbc.edu/lug-mailing-list/2003-06/msg00017.html)

On Mon, Jun 09, 2003 at 01:04:43PM -0400, Mario M. Butter wrote:

> Kevin Zembower wrote:
> >I'm having problems getting ftp to work through my Linksys DSL 8-port
> >router.

> In "non-passive" ftp sessions, when you ask for data (including a
> dir), the ftp server tells the client which port it will available
> on, and expects the client to make a new connection to that
> port. The new port for the data is ever-changing, so most
> inexpensive routers don't handle it. In "passive" ftp sessions, the
> data is sent on the same port as the commands. You need to turn on
> passive mode to get it to work properly.

No.

In both passive and active FTP modes, data is sent on a separate port
from the command port. The difference is who initiates the data
connection. In active mode, the server initiates the data socket
("calling back" to the client); in passive mode, the client initiates
a second connection for the data socket. This is a problem for two
reasons; (1) firewalls; (2) NAT. The DSL router probably does NAT and
no firewalling, so let's focus on NAT.

The problem with NAT is that your inner device is not directly
addressable. So, if you run an FTP client behind a NAT device, active
mode can't work because the server outside the NAT device can't
address it. If you run an FTP server behind a NAT device, you have
the opposite problem; active mode should work fine because the server
can connect back to the client, but passive mode doesn't work because
the IP that the server passes to the client makes no sense to the
client. "Smart" NAT devices (such as Linux iptables/ipchains/ipfwadm
with the right modules loaded) fix this by also translating the
address in the FTP application-layer packet.

If dumb NAT is on client-side, use passive mode. If dumb NAT is on
server-side, use active mode. If dumb NAT is on both side, you're in
trouble.

To further complicate matters, some FTP clients only support one or
the other. For example, many version of the Solaris FTP client only
support active mode, while web browsers prefer passive mode.

That said, there are sometimes some tricks you can use to support
passive mode on a server behind a dumb NAT, but you need to research
them carefully; misuse will create giant security holes.

- Morty